In order to use wood a source of energy, wood chips can be dewatered and subsequently used as fuel. To remove water from the wood chips, the wood chips may be subjected to heat that causes moisture in the wood chips to evaporate. However, such methods are time-consuming and require large amounts of energy which makes such methods less effective in terms of energy economy. A method which is more economical in terms of energy economy is to dewater the wood chips by means of compression. In an article published 2010 by “ScienceDirect”, Dewatering of high-moisture wood chips by roller compression method (Takahiro Yoshida, Hiroyuki Sasaki, Tsutomu Takano and Osamu Sawabe), a method of dewatering wood chips by roller compression was disclosed. In that article, a method was described in which wood chips were compressed between rolls. The article discloses an apparatus with a primary and a secondary unit that both included rollers. The secondary unit had a lower roller with holes having a diameter of 6 mm that were intended to allow squeezed-out water into an aspiration funnel attached inside the roller. The water was reportedly expelled by an exhaustion fan attached to the back of the apparatus. A stainless steel wire mesh belt around the lower roller allowed water to flow from the chips to the holes. The chips included cedar and cypress chips. Wood chips were dewatered at pressures of 10, 20 and 30 MPa. It was found that roller compression can remove water from wood chips with low energy consumption.
GB 2090954 A discloses a method and an apparatus in which wood chips are dewatered between two endless conveyors between which the wood chips are squeezed. One of the conveyors is a perforated conveyor and a suction means may be provided for applying a reduced pressure or vacuum to the underside of the perforated conveyor.
When compression has been used to dewater wood chips, the effect has not always met expectations. Therefore, it is an object of the present invention to improve processes in which dewatering of wood chips is carried out by means of compression. In particular, it is an object of the invention to provide an apparatus and a method in which a high degree of dewatering can be achieved such that the moisture content after pressing will be low.